People have been concerned with how to cool the rotating elements of a superconductor magnet. High temperature superconductor magnets typically need to be cooled to a temperature of about 20-77 K during use.
It is known to place a cryocooler in the rotating reference frame of the magnet to cool the magnet windings. It is also known to force circulate a fluid between a stationary refrigerator and a rotating field winding.
According to one aspect of the invention, a system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located.
Embodiments of this aspect of the invention may include one or more of the following features.
The closed circulation system includes a heat transfer assembly located in the rotating reference frame. A heat transfer gap is defined between the cryocooler and the heat transfer assembly. Heat is transferred from the superconductor device to the heat transfer gap by the heat transfer assembly. A coolant, for example, helium, is located in the heat transfer gap.
In illustrated embodiments, the rotating heat transfer assembly includes a heat pipe having a first fluid path for directing a flow of liquid coolant, for example, liquid neon, from a cold end to a warm end of the heat transfer assembly, and a second fluid path for directing a flow of gas coolant, for example, neon gas, from the warm end to the cold end of the heat transfer assembly.
A warm end conduction block is mounted to the superconductor device and the heat pipe. The warm end conduction block defines the warm end of the heat transfer assembly. A cold end conduction block is mounted to the heat pipe and defines the cold end of the heat transfer assembly. The cold end conduction block includes a first plurality of fins and the cryocooler includes a second plurality of fins intermeshed with the first plurality of fins. The cold end conduction block fins are rotatable with respect to the cryocooler fins. Space between the intermeshed fins defines the heat transfer gap.
In particular embodiments, a cooldown path containing, for example, liquid nitrogen or liquid oxygen, is provided to cool the superconductor device prior to rotation of the superconductor device.
The cryocooler can include a plurality of coldheads. A heat pipe extends from the plurality of coldheads. The heat transfer gap is defined between the heat pipe and the heat transfer assembly.
In particular embodiments, a coldhead of the cryocooler is located within an insulated enclosure. A rotatable shaft of the superconductor device extends into the enclosure. A cold end of the shaft includes a condenser having a first plurality of fins. The coldhead includes a second plurality of fins intermeshed with the condenser fins. The condenser fins are rotatable with respect to the coldhead fins.
In an other embodiment, a stationary cryocooler is positioned within a rotatable shaft of the superconductor device. The rotatable shaft defines flow channels for liquid coolant. The cryocooler includes an extension and coolant in the closed circulation system condenses upon contact with the extension. The extension is radially aligned with the superconductor coils of the superconductor device.
The closed circulation system includes a fluid path for delivering liquid coolant from a surface of the cryocooler to the superconductor device, and a second fluid path for returning coolant vapor from the superconductor device to the surface of the cryocooler.
According to another aspect of the invention, a superconductor rotor cooling system includes a cryocooler located in a stationary reference frame and a heat transfer assembly located in a rotating reference frame. A heat transfer gap defined between the cryocooler and the heat transfer assembly transfers heat from a superconductor device located in the rotating reference frame to the heat transfer gap.
According to another aspect of the invention, a method of cooling a superconductor device includes the steps of locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.
According to another aspect of the invention, a method of cooling a superconductor device includes the steps of locating a cryocooler in a stationary reference frame, locating a heat transfer assembly in a rotating reference frame, and transferring heat from a superconductor device located in the rotating reference frame through the heat transfer assembly to a heat transfer gap defined between the cryocooler and the heat transfer assembly.
Among other advantages, the cooling system of the invention permits the cryocooler to remain stationary while eliminating the need for an extensive sealing system needed to flow coolant through an open circulation system. The heat transfer gap provides an efficient structure for transferring heat from the superconductor device to the cryocooler.